Vertical water distribution during the drying of polymer films cast from aqueous emulsions |
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Authors: | J-P Gorce D Bovey PJ McDonald P Palasz D Taylor JL Keddie |
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Institution: | (1) Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK, GB;(2) ICI Paints, Wexham Road, Slough, Berkshire SL2 5DS, UK, GB |
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Abstract: | We present a systematic study of the vertical uniformity of water distribution during the drying of waterborne colloidal films,
testing the predictions of a Peclet number Pe defined for this system. Pe indicates the relative contributions of water evaporation and Brownian diffusion in determining the concentration profile
in the vertical direction (i.e. normal to the substrate). When Pe < 1, the water concentration in films cast from an alkyd emulsion is found via magnetic-resonance profiling to be uniform with depth, which is consistent with expectations. When Pe > 1, a gradient in the water concentration develops, with less water near the interface with air. The water profiles reveal
that the alkyd particles do not coalesce immediately upon contact in close-packing. At later times, a concentrated surface
layer develops, but particles are not coalesced in this layer to form a continuous “skin”, but rather the structure is likely
to be that of a biliquid foam.
Received 20 March 2002 and Received in final form 12 June 2002 |
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Keywords: | PACS 82 70 Kj Emulsions and suspensions – 76 60 Pc NMR imaging – 47 55 Mh Flows through porous media |
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